Embroider: Use of ember internals

[fsmanuel]

This topic got raise by @Pixelik in #733. I did some digging but figured I don't have enough knowledge about embroider. So all help is appreciated!

In an efford to have all the findings in one place, here is what I found:

The genesis of addon/-private/ember-internals.js:

• Support ember 3.10, drops support for decorators #641 added the code to make it work for ember >= 3.10
• Support Ember 3.13 (redux) #668 made it work for ember >= 3.13
• 89d8307 I changed it to import __EMBER_METAL__ from '@ember/-internals/metal/index';

So I have two assumptions:

1. The internal import does not work for Embroider
2. The internal import is stable since ember 3.13 and we no longer need the fallback implementations

Now my question is, how do we get the import embroider safe or even better remove it altogether? I found:

• Use require instead of import to make Embroider happy qonto/ember-cp-validations#20

We already borrowed a lot of the changes in the qonto fork so if this solution is still recommended by the embroider team I would say we use require and refactor the internals like I proposed here: #735 (comment) (maybe we don't even need the fix from @Pixelik)

The same goes for import { meta } from '@ember/-internals/meta';

//cc @ef4 @gilest